e1000: Fix filling skb descriptors while using packet split

-  Simplified by calling skb_fill_page_desc(), which is more efficient.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: John Ronciak <john.ronciak@intel.com>